<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box{
            width: 100px;
            height: 100px;
            background-color: khaki;
            margin: 5px;
        }
        .box:hover{
            outline: 5px solid red;
            outline-width:5px;
            outline-style:dashed;
            outline-color:blue;
            /* 
            只有三个小属性：
            outline-width：10px
            outline-style:dashed
            outline-color:blue           
            */


        }
        /* input:focus{
            outline: 5px solid red;
        } */

        input:focus{
            outline: none;
        }
    </style>
</head>
<body>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>

    <input type="text" />
    <input type="text" />
    <input type="text" />
</body>
</html>